using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Transport;

namespace ZB.MOM.WW.ScadaBridge.DeploymentManager;

/// <summary>Recomputes deployment revisions from authoritative configuration on every probe.
/// Process-local watermarks cannot prove freshness after another central changes the shared store,
/// so nothing is memoised across calls.</summary>
public sealed class StaleInstanceProbe : IStaleInstanceProbe
{
    private readonly IFlatteningPipeline _flatteningPipeline;

    /// <summary>Initializes the authoritative probe.</summary>
    /// <param name="flatteningPipeline">The pipeline used to flatten instances for staleness comparison.</param>
    public StaleInstanceProbe(IFlatteningPipeline flatteningPipeline)
    {
        _flatteningPipeline = flatteningPipeline ?? throw new ArgumentNullException(nameof(flatteningPipeline));
    }

    /// <inheritdoc />
    public async Task<string?> GetCurrentRevisionHashAsync(int instanceId, CancellationToken cancellationToken = default)
    {
        // Hash only: staleness never reads the validation result.
        var result = await _flatteningPipeline.ComputeRevisionHashAsync(
            instanceId, _flatteningPipeline.CreateSession(), cancellationToken).ConfigureAwait(false);
        return result.IsSuccess ? result.Value : null;
    }
}